This invention is generally in the field of the manufacture of cans for containing perishable foods and a variety of other products in a hermetically sealed state. More specifically the invention concerns a method of, and means for, detecting uncoated regions in the annular coatings of sealing composition on can end disks preparatory to their attachment to can bodies.
The sanitary can in general is made up of a body and a pair of end disks closing its opposite ends. The can body is side seamed and flanged at both ends. The end disks have curled peripheral rims which are coated with a sealing composition. When the can body flanges and end disk rims are machine folded together, the composition provides a tight, gasketlike seal. The can body is delivered to the food packer or any other filling machine with one end sealed; the other end is sealed when the can is filled. Thus, for hermetically sealing the can ends, it is essential that the sealing composition be applied as a uniform coat on the curled rims of the end disks. The end disks that have been coated improperly with the sealing composition must therefore be detected and rejected prior to attachment to can bodies.
To this end it has been suggested and practiced to mount a pair of light sensitive devices in transversely spaced positions over a conveyor transporting a succession of coated can end disks from the coating station to the next processing station. The pair of light sensitive devices operate conjointly to detect uncoated regions on the curled rims of the can end disks. This conventional practice is unsatisfactory, however. The light sensitive devices over the conveyor can certainly detect can end disks whose rims are totally or half uncoated, but not those having smaller uncoated regions. Passing undetected, the latter kind of end disks are allowed to be attached to can bodies to create cans that are not sealed hermetically.